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Chemistry I Accelerated
Study Guideline - Chapter Four
Atomic Structure
________________________________________________________
By the end of this chapter the skills you should be able to demonstrate
are:
1. Discuss scientists and experimental contributions to the development
of atomic theory.
2. Explain the laws of multiple proportions and definite proportions and
give examples.
3. Compare and Contrast Dalton’s, Thomson’s, and Rutherford’s
model of the atom.
4. Distinguish among protons, electrons and neutrons in terms of their
relative masses and their charges.
5. Describe the modern conceptual model of the atom, including the
properties of the major subatomic particles.
6. Explain how the atomic number identifies an element.
7. Identify the number of protons, neutrons and electrons in an atom
when given the atomic number (Z), mass number (A) and charge.
8. Demonstrate the relationship between the atomic mass of an element
and the isotopes of that element.
9. Calculate the average atomic mass of an element from isotope data.
Suggested Problems: p. 122-124
p. 125
#46, 52, 54, 64, 70, 76, 82
#7, 8, 9
Video: World of Chemistry - The Atom
Please Answer the following question while you watch the video
1. What did Democritis propose?
2. What did Dalton propose?
3. What are the three basic particles of the atom?
4. What are the two regions of the atom?
5. What determines the identity of an atom?
6. How many electrons does an atom have?
7. What is a STM? What can you see with it?
8. What do opposite charges do? What do like charges do?
9. What was Rutherford’s surprise?
10. What Did Rutherford conclude from this surprise?
page 2
Bill Nye - The Atom
Please Answer the following question while you watch the video
1. What is the smallest piece of matter?
2. What are the parts of the atom?
3. What parts of the atom are in the nucleus?
4. What is the charge on a Proton? Neutron? Electron?
5. What is an atom mostly?
6. All matter is made of what?
7. What is produced when you pass electricity through water (electrolysis)? How many parts of hydrogen gas
and oxygen gas do you get from the electrolysis of water?
8. Why is the volume of 2 cups of water greater than the volume of 1 cup of water plus one cup of alcohol?
9. What makes one element (atom) different from another?
10. What is the atomic number?
Discovering Atomic Structure
1. The negatively charged electrode of a cathode ray tube is called the _______________.
a. anode
b. cathode
c. plate
d. magnet
2. The physicist Henri Becquerel discovered radioactivity while studying the phosphorescence of
____________.
a. radium
b. silicon
c. uranium
d. curium
3. Which of the following is not a type of radiation?
a. alpha
b. beta
c. gamma
d. delta
4. Rutherford alpha scattering experiment showed that the nuclear charge must be ______________?
a. positive
b. neutral
c. negative
d. too small to be detected
5. Thomson concluded that cathode rays were composed of particles that were ______________?
a. positive
b. heavy
c. negative
d. visible
page 3
The Milikan Oil-Drop Experiment
In 1909, the American physicist Robert Milikan measured the size of the charge of an electron. Using the
apparatus illustrated below, he introduced a fine mist of oil into a closed chamber. The droplets of oil passed
between two electrically charged plates through which he was able to influence their rates of decent.
Observing the individual droplets through a microscope, Milikan was able to adjust the electrical force so that
the drops moved away from whichever plate had the same charge. He timed the drops’ ate of movement.
From this information, he was able to determine both the charge of an electron and to suggest a value for its
mass. Study the illustration below and answer the following questions.
_____1. To cause a negatively charged oil droplet to move upwards; plate Y should have _______________.
a. a positive charge
b. a negative charge c. an excess of protons
d. an excess of neutrons
_____2. The purpose of device Z is to _______________.
a. observe the electrical potential difference (voltage) between the plates
b. separate spectral emissions
c. magnify droplets of liquid
d. locate positively charged particles
_____3. If a droplet was momentarily suspended between the electric plates, ________________________.
a. the number of protons in the droplet equaled the number of electrons
b. there was no charge on the plates
c. the droplet weight was exactly balanced by forces of electrical repulsion/attraction
d. the mass of the electrons in the droplet equaled the mass of the protons
_____4. The function of device W is to ________________________.
a. remove excess mist
b. supply protons
c. monitor relative humidity
d. produce a mist from liquid oil
_____5. If electrical leads to plates X and Y were reversed, negatively charged oil droplets that had been
moving upwards would ________________________.
a. remain suspended
b. move downwards towards plate Y
c. move upwards towards plate X
d. acquire a positive charge
page 4
The Rutherford Experiment
Our modern view of atomic structure is based to a large extent on the wok that British scientists
Rutherford and Geiger did in 1911. In the classic experiment, positive alpha particles bombarded a sheet of
gold foil. The paths that followed by those particles are illustrated in the diagram below.
Path
Path
Path
Path
Atom
1
Nucleus
2
3
4
_____1. Which of the four path was most common?
a. one
b. two
c. three
d. four
_____2. Which of the four path was least common?
a. one
b. two
c. three
d. four
_____3. Path two was a straight line because of the alpha particles’ _____________________.
a. magnetic repulsion
b. high velocity
c. distance from the gold nuclei
d. interaction with electrons
_____4. Path four will most likely _____________________.
a. never be observable
b. be characteristic of only the fastest moving alpha particles
c. be characteristic of alpha particles that move directly towards a nucleus
d. result in an atomic reaction
_____5. When Rutherford analyzed his results, he suggested that _____________________.
a. the atom was mostly empty space
b. atoms contained a small dense center
c. the atomic center was positive in charge
d. all of the above were true
page 5
Matching
On the left, write the term or the name from the list that matches the description
alpha particle
atomic nucleus
Becquerel
cathode ray
Curie
Dalton
electron
gamma radiation
Joliot-Curie
Milikan
radioactivity
Rutherford
Thomson
Chadwick
Geiger
static electricity
_____________________________1. electrical charges that are not in motion.
_____________________________2. stream of particles originating from a cathode
_____________________________3. proposed the first atomic model that accounted for the electrical
nature of the atom
_____________________________4. measured the size of the charge on an electron
_____________________________5. suggested that alpha particles might be rebounding at an angle
approaching 180° after coming close to the nucleus
_____________________________6. spontaneous emission of radiation from an element
_____________________________7. radiation that is similar to X-rays and not composed of particles
_____________________________8. proposed that the atom was a sphere that was of equal density all the
way through
_____________________________9. discovered a neutral beam that had high penetrating power.
_____________________________10. was surprised when alpha particles bounced back
_____________________________11. small core at the center of the atom containing a positive charge
_____________________________12. radiation that has a +2 charge
_____________________________13. is credited with the discovery of radioactivity
_____________________________14. discovered the radioactive element polonium
_____________________________15. was first to identify the neutron
Draw and label a diagram of Dalton’s, Thomson’s and Rutherford’s model of the atom.
page 6
Nuclear Symbols
Element symbols are often accompanied by notation that gives information on atomic composition. The
subscript, written to the lower left of an element symbol, represents the atomic number. The superscript,
written to the upper left of the symbol, represents the mass number or the total number of protons and
neutrons. Using this information, complete the following table.
Symbol
12
40
127
23
20
48
40
238
6
18
53
11
10
22
20
92
C
Ar
I
Na
Ne
Ti
Ca
U
Atomic #
Mass #
# of protons
# of neutrons
# of electrons
1. How many protons and electron in a neutral
vanadium atom?
2. How many protons and electron in a neutral
potassium atom?
3. How many protons and electron in a neutral
platinum atom?
4. What is the name of the element that contains 17
protons?
5. What is the name of the element that contains 82
protons?
6. Write the complete chemical symbol for the atom
that contains 84 protons, 125 neutrons and 80
electrons?
7. Write the complete chemical symbol for the atom
that contains 27 protons, 32 neutrons and 25
electrons?
8. Write the complete chemical symbol for the atom
that contains 73 protons, 108 neutrons and 68
electrons?
9. Write the complete chemical symbol for the atom
that contains 31 protons, 39 neutrons and 28
electrons?
page 7
Complete the following table:
59
2+
140
Ni
Symbol
3+
Ce
28
58
91
4+
Zr
40
79
2–
Se
34
14 4–
C
6
45
3+
Sc
21
Protons
Neutrons
Electrons
Hydrogen Isotopes
Atoms are made up of subatomic particles, such as protons, neutrons and electrons. The nuclei of atoms
that make up isotopes of an element differ. There are three known isotopes of hydrogen. Make a drawing
that represents each of these isotopes.
e
2p
2n
e
Helium-4
Protium
Hydrogen-1
Deuterium
Hydrogen-2
Tritium
Hydrogen-3
1. Do the numbers of electrons for neutral isotopes of the same elements differ? ________
2. Do the number of protons for such isotopes differ? __________
3. Do the number of neutrons for such isotopes differ? __________
4. Do the atomic numbers for such isotopes differ? Explain.
5. Do the mass numbers for such isotopes differ? Explain.
6. If (1 + 2 + 3)/3 = 2 then why is the average atomic mass for hydrogen 1.0079 and not a whole number?
page 8
Review Activity - Development of Atomic Theory
atom
Dalton
energy level
neutron
quantum
atomic number
definite proportions
isotope
multiple proportions
Rutherford
Bohr
Democritis
Lavoisier
Planck
Thomson
Chadwick
conservation of matter
Einstein
electron
mass number
nucleus
proton
Proust
subatomic particle
More than 2000 years ago, a Greek philosopher named _____________ proposed the existence of very
small, indivisible particles, each of which was called a(n) _____________. The theory that such particles
existed was supported much later, by _____________ who proposed, in his law of _______________ _____
__________, that matter could not be created or destroyed. Then ___________ proposed, in his law of
____________ _____________, that the ratio of the masses of elements in any given compound is always the
same. The law of _____________ ______________ , proposed soon after, states that the masses of one
element that combine with a fixed mass of another element in different compounds are in simple, wholenumber ratios. An atomic theory based on these laws was developed by _____________, who is credited with
the first modern atomic theory
It was later proposed that the atom is in fact divisible into smaller parts each of which is called a(n)
___________ ____________. These particles include the negatively charged ____________, discovered by
____________; the positively charged ____________; and the uncharged ____________, discovered by
____________. The latter two particles are present in the ____________, or center of the atom, which was
discovered by ____________ in his gold foil experiments.
The number of positively charged particles in an atom is called its _________ __________. The total
number of positively charged particles and the uncharged particles is called the atom’s _________ ________.
An atom that has the same number of positively charged particles as another atom, but a different number of
uncharged particles, is called a(n) ____________.
The Danish physicist ____________ proposed a model of the atom in which electrons orbit the nucleus
without losing energy. He called each possible orbit a(n) ___________ _________. He based his theory to
some extent on the work of ____________, who proposed that light is made up of units of energy of a
definite amount, each of which is called a(n) ____________ of energy.
page 9
Average Atomic Mass Problems
1. What is the average atomic mass in AMU of the element copper if it is composed of 69.5% of an isotope of
atomic mass 63.00 and 30.5% of an isotope with a atomic mass of 65.00?
2. Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following atomic
masses and abundances in nature: 7.30%, 6.017AMU and 92.7%, 7.018AMU
3. Calculate the average atomic mass of chromium, given the following percent abundances and atomic
masses: 4.350% 49.946AMU; 83.790% 51.941AMU; 9.500% 52.941AMU; 2.360% 53.939AMU.
Analyzing a Spectrograph (Mass Spectrometer)
A mass spectrograph (spectrometer) is an instrument used to separate an elements isotopes and to measure
their relative abundances. Within this device, beams of an element’s ions are passed through a strong
magnetic field. As they are passed through, they respond to the magnetic force. Ions of greater mass possess
more inertia, or more of a tendancy to continue to move in a straight line, and so deviate only slightly from
their projected path. Ions of lesser mass are more greatly influenced by the field and demostrate greater
deviation. Examine the three mass spectrographs illustrated below and answer the questions that follow. Note
that the upper scale of each spectrograph shows the atomic mass in AMU. Below each spectrograph the
percent abundance of each isotope is indicated.
Atomic Mass
30.0
29.0
28.0
27.0
26.0
25.0
24.0
23.0
A
Relative %
100.0
1. a. What is the atomic mass of the isotope of the element represented by spectrograph A? _____________
b. What are the name and the element symbol of element A?
_____________
page 10
Atomic Mass
30.0
29.0
28.0
27.0
26.0
25.0
24.0
23.0
B
Relative %
11.17 10.13 78.70
2. a. Based on the experimentally obtained data in spectrum B calculate the average atomic
mass of this element. Show your work.
_____________
b. Which isotope deviated most from its straight line path?
c. What are the name and the element symbol of element B?
Atomic Mass
56.0
55.0
54.0
53.0
52.0
51.0
_____________
_____________
50.0
49.0
C
Relative %
2.38 9.55 83.76
4.31
3. a. Based on the experimentally obtained data in spectrum C calculate the average atomic
mass of this element. Show your work.
_____________
b. Which isotope deviated most from its straight line path?
c. What are the name and the element symbol of element C?
Atomic Mass
_____________
_____________
202.0 203.0 204.0 205.0 206.0 207.0 208.0 209.0
D
Relative %
1.37
26.26 20.82 51.55
4. Based on the experimentally obtained data in spectrum D calculate the average atomic
mass of this element. Show your work.
page 11
_____________
Nuclear Stability
The stability of a nucleus is dependent upon the ratio of its component particles. Complete the following
table of stable nuclei. Determine the neutron-to-proton ratio of each (to one decimal point) and then plot the
points on the grid provided at the bottom of the page.
Neutron-toNeutron-toIsotope
Protons
Neutrons
Isotope
Protons
Neutrons
proton ratio
proton ratio
4
2
79
He
Br
35
12
90
6
40
16
98
8
42
C
Zr
O
Mo
20
107
10
47
27
127
13
53
35
138
17
56
40
142
20
60
56
158
26
65
58
174
28
70
Ne
Al
Cl
Ca
Fe
Ni
Ag
I
Ba
Nd
Tb
Yb
Neutron-to-Proton ratio
1.5
1.0
0.5
Atomic Number
5
10
15
20
25
30
35
page 12
40
45
50
55
60
65
70
75
Challenge Problems - Chapter 4
1. Lithium has two naturally occurring isotopes. Lithium 6 has an atomic mass of 6.015 AMU; lithium-7 has
an atomic mass of 7.016 AMU. The average atomic mass of lithium is 6.941 AMU. What is the
percentage of lithium-7 in nature?
2. Bohr’s atomic theory can be used to calculate the energy required to remove an electron from an orbit of a
hydrogen atom or an ion containing only one electron. This is the ionization energy for that atom or ion.
The formula for determining the ionization energy E is:
E = Z2 • k
n2
where Z is the atomic number, k is 1312 kJ per mole, and n is the energy level. How much energy is
required to eject an electron from a hydrogen atom when the electron is in the ground state (n=1)? In the
second energy level? How much energy is required to eject a ground state electron from Li2+?
page 13
Composition of the Atom - Word Scramble
Use the clues provided to help you unscramble the letter to form words related the development of atomic
structure. The letters in the circle spell out, in order, the name of a famous chemist.
CLUES
1. Pieces of inert metal connected to a power source
2. Element discovered by Marie Curie
3. Atoms with the same atomic number but different mass numbers
4. Radiation consisting of a high speed Helium nuclei
5. Center of the atom
6. Subatomic particle with no charge
7. Element with a mass number of 19.0
8. A mass __________________, a device used to determine atomic masses. (If you can’t get this one
look at the page before the challenge problems for a hint).
9. A positively charged particle
10. Element with an atomic number of one.
1. T E R D L C E E O
__ __ __ __ __ __ __ __ __
2. L O M U O P N I
__ __ __ __ __ __ __ __
3. S O O S T I P E
__ __ __ __ __ __ __ __
4. H A A L P
__ __ __ __ __
5. S U C U N E L
__ __ __ __ __ __ __
6. N E T N O U R
__ __ __ __ __ __ __
7. N E O L I R F U
__ __ __ __ __ __ __ __
8. E P R T G S C H P O R A
__ __ __ __ __ __ __ __ __ __ __ __
9. T O R N O P
__ __ __ __ __ __
10. O G Y D N E H R
__ __ __ __ __ __ __ __
Name ____________________________
page 14